Processes for industrial production of acetic acid that have been realized include a process using oxidation of acetaldehyde, a process using a reaction of methanol and carbon monoxide and a process using oxidation of lower paraffins. Processes for industrial production of ethyl acetate that have been realized include an esterification reaction of ethanol and acetic acid, and a dimerization reaction of acetaldehyde.
In recent years, various production processes for acetic acid using ethanol as the starting material have been studied as an alternative.
An example of a process for obtaining acetic acid from ethanol in a single stage which employs copper oxide as the main catalyst in combination with zinc oxide, chromium oxide and (chromium oxide-manganese oxide) (Japanese Unexamined Patent Publication No. 57-102835) has been disclosed. However, this process has been difficult to apply on an industrially practical scale because the reaction temperature is high at 260-360° C., and the acetic acid selectivity is not sufficient.
Oxidation processes with catalysts of platinum group metals, particularly palladium, have also been disclosed. For example, acetic acid can be obtained by reacting a catalyst of metallic palladium or palladium loaded on a carrier such as silica or alumina (Japanese Examined Patent Publication No. 48-19292, Brazil Patent BR-9104562) with ethanol and oxygen. Palladium catalysts offer the advantage of a relatively low reaction temperature of 100-200° C. However, these processes have all had the drawback of abundant by-products such as acetaldehyde and carbon dioxide, which have lowered the yield of the target acetic acid.
Processes using metallic palladium-loaded catalysts have been disclosed as processes for obtaining ethyl acetate from ethanol by a single stage. For example, according to Kunugi and Matsuura et al. (Kogyo Kagaku Zasshi, Vol. 71, No. 9, p. 1517 (1968)), ethyl acetate is obtained from ethanol and oxygen in the vapor phase using a catalyst of metallic palladium loaded on a carrier of active carbon, γ-alumina or the like. Ethyl acetate is also obtained from ethanol and oxygen using a metallic palladium/γ-alumina catalyst (Brazil Patent BR-8901776). However, these processes have had the disadvantage of a low conversion rate of ethanol and abundant by-products such as acetaldehyde, methane and carbon dioxide, which have lowered yields of the target ethyl acetate.
There has also been disclosed a catalyst including a palladium component and crystalline titanium pyrophosphate represented by (TiP2O7) (Japanese Unexamined Patent Publication No. 4-300851). Here, improvement in ethyl acetate production activity has been reported by use of this binary catalyst having palladium and titanium pyrophosphate as essential components, but even this process has low ethyl acetate production activity and selectivity, and is inadequate in practical terms on an industrial scale.
On the other hand, processes employing palladium as the catalyst allow acetic acid and/or ethyl acetate to be obtained from ethanol and oxygen under relatively mild reaction conditions. Notwithstanding, for industrial scale production, a catalyst that is capable of catalyzing the reaction with even higher activity and higher selectivity is strongly desired.